 	   (for ~bindings
 	     (double ~expr))))
 
-;; Repulsive Energy
+;; Repulsive Energy and Force
 
 (defn- node-line-distance
   "Returns the distance from node to the line between [x_1, y_1] and [x_2, y_2]."

		       {:inf-irrs seq-of-inf-irrs,
			:upper-neighbours-of-inf-irrs upper-neighbours})))))

;; Force Layout

(defn force-layout

  (sum [[x y] node-connections]
       (double (line-length-squared (node-positions x) (node-positions y)))))

(defn- attractive-force
  "Computes the n-th component of the vector of attractive forces
  acting on the inf-irreducible elements of layout. The vector
  itself has 2n entries."
  [layout inf-irrs n]
  (throw (UnsupportedOperationException. "Not yet implemented.")))

;; Gravitative Energy and Force

(defn- phi
  "Returns the angle between a inf-irreducible node [x_1,y_1]
